This invention relates to a gear rack for propelling a mining machine used for underground mining wherein the gear rack includes a plurality of rack segments each having a hole in each of the opposite ends. The holes in adjacent ends of rack segments engage a support member and receive a fastener to form a flexible connection to allow limited motion lengthwise of the rack segments while rack teeth on both sides of the rack segments mesh with spur gears of a winch drive on the mining machine.
In West German patent publication No. 26 27 684, there is described a feeding mechanism for a mining machine constructed in the form of a gear rack and made up of rack segments. Tube-shaped portions of the gear racks are joined in a flexible manner such that adjacent ends of the rack segments are placed on the same support and contain a hole at the lower surface of each end for engagement with a support. The support engages from below the rack segment which can move lengthwise to a limited degree within a guide rail bounded by supports on the side. A bolt is used to connect end portions of the gear racks with a support to facilitate the formation of flexible joints and provide limited lengthwise motion. The mining machine which moves along a conveyor meshes with equally-spaced attachments on both sides of the gear rack segments. The attachments comprise a rotatable bolt in a hole located within a horizontal plane of the gear rack and perpendicular to the directin of motion by the mining machine. Protruding ends of the rack segments extend from the tube-shaped gear rack profile. The bolts for each rack segment are fixed in an axial direction by a device which is common to all the bolts. A portion of each bolt is designed to permit engagement with the device which substantially fixes the protruding portions of the bolts from the tube-shaped portions of the rack. Both ends of the rack segments have the shape of a sphere.
Gear racks suffer great wear because of the operating conditions existing in underground mining operations and because of the great stress imposed on the mining machine. Wear of the rack occurs mainly at such locations where the teeth of the driving gear wheel make contact with the teeth of the gear rack. These locations comprise the contacting surfaces between the driving pins and the flank segments of the gear teeth. Because of the connection with the rack support parts, the gear racks known in the art do not permit turning the rack segments 180.degree. for continued use of a single gear rack segment such that the lower halves of the driving pins can be utilized for meshing engagement with the teeth of the driving wheel of the mining machine.